“They would be interested to know what can be achieved through cyber-warfare and this will have shown them how devastating an attack like this can be.

“If they can bring the NHS to its knees for three days and there is then a terror attack, there would chaos.”

He added: “I would have expected the Trust to have been running a mirrored system at a disaster recovery centre, which would allow them to switch over immediately in the event of problems.

“They either didn’t have this back-up service – which is surprising – or something prevented them kicking it into action in the usual way.”

The Department of Health said it was not the first cyber-attack on a hospital trust in England but refused to give details on the frequency of such incidents.

A spokesman said it was looking at measures to “reduce vulnerability to cyber-attacks and reduce the impact of a data security incident, if it does occur.”

Almost all planned ops and outpatients appointments were cancelled at the hospitals in Grimsby, Scunthorpe and Goole for three days after the attack (file image)

He added: “We are determined to help all health and NHS organisations improve cyber security and will learn lessons from this incident.”

Karen Dunderdale, deputy chief executive of the North Lincolnshire trust, said most of its computer systems were running by late Wednesday.

IT experts were still working on a few affected areas yesterday.

Ms Dunderdale added: “I would like to take this opportunity to apologise to everyone who has had their appointment cancelled this week.

“We will of course be rescheduling them as soon as possible, with those patients identified as clinically urgent seen first.

“I would also like to take this opportunity to thank all of our staff for their dedication and hard work during this major incident as they have worked tirelessly to ensure our patients have been safely cared for during this time.”

An NHS Digital spokesman said: “This issue highlights the fact that there are threats to data security within the health and care, as with any other sector.

“We remain committed to supporting the protection of data with the highest possible security standards, high levels of security expertise from the centre and appropriate training and awareness of the risks for all staff.

“Our alerts are designed as a call for organisations to take sensible action and are not a cause to panic.

“We have no evidence that this is anything other than a local isolated incident but we will continue to keep health and care organisations informed.”

News of the attack emerged a day after Chancellor Philip Hammond restated the government’s aim to spend £1.9billion over five years to underpin its national cyber security strategy.

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